As we describe in our U.S. Pat. No. 5,538,207, which issued Jul. 23, 1996 for our Boom-Mountable Robotic Arm, high voltage transmission and distribution lines are typically strung between a series of spaced-apart support structures or poles. The conductors are connected to insulators mounted on or suspended from cross arms extending at the upper end of transmission or distribution poles, or conductor support points built into transmission structures. Periodically it is necessary to replace or repair the poles or structures, cross arms and insulators to maintain the electrical circuit in good working order. It is preferable if this maintenance and repair work can be performed without de-energizing the conductors in order to avoid an interruption of service to consumers, or to avoid the necessity of purchasing power from an alternative source, or other system disruptions.
Hot line repair work is a potentially hazardous undertaking. Safety regulations require that linemen maintain a minimum work clearance or “limit of approach” from energized conductors. The limit of approach varies depending upon the voltage of the conductors in question.
Conventional procedures used by linemen to temporarily support energized conductors in order to enable repair of damaged or obsolete components involve the use of insulated wire tongs, lift poles and rope blocks in labour-intensive, complex rigging arrangements. Conventional fiberglass insulated tools are limited to use only in good weather. Any accumulation of moisture which may impair their insulating property requires that the job be stopped, and that the conductors be placed in an insulator which is rated for all-weather use.
Fujimoto in U.S. Pat. Nos. 5,107,954 and 5,183,168 which issued respectively on Apr. 28, 1992 and Feb. 2, 1993 describes an operator cabin mounted on the distal end of a vertical mounted boom, the operator cabin having at least one manipulator operatively connected to the front side of the cabin. A pair of manipulators are illustrated. The manipulators are adapted to manipulate electrical components while energized. In applicant's view the device of Fujimoto appears to be limited to electric components having a relatively lower voltage, for example, 46 kV and below.
Several auxiliary cross arms have also been proposed in the past for temporarily supporting conductors, thereby reducing the need for labour-intensive “stick work” by linemen. For example, U.S. Pat. No. 4,973,795, which issued to Sharpe on 27 Nov. 1990, relates to an auxiliary cross arm consisting of an insulated boom fitted with polymer insulators and conductor hooks for releasably engaging energized conductors. The Sharpe boom is suspended from a crane above the transmission lines to be serviced.
Auxiliary cross arms for temporarily lifting and supporting energized conductors from below are also well known. Such cross arms typically have sleeves which are connectible to the boom jibs of derrick or bucket trucks.
As we also describe in our U.S. Pat. No. 6,837,671, which issued Jan. 4, 2005 for our Apparatus for Precisely Manipulating Elongate Objects Adjacent to and such as Energized Overhead High Voltage Transmission Lines, the replacement and installation of cross arm members or insulators on overhead transmission towers is generally accomplished, whenever possible, while the electrical transmission lines are energized. It is common to find several rows of transmission structures supporting two or more vertically separate electrical transmission lines located in relatively close proximity. This confined overhead working area emphasizes the need for the precise elevating and manipulation of objects so as to avoid accidental arcing between the energized lines and the object with obvious dire consequences to workmen and machinery. A convenient practice is to employ a helicopter to elevate such objects to workmen on the tower. However, where a structures supports vertically separated energized lines, wind gusts and rotor downwash make this practice difficult and may require the de-energizing of a portion of the electrical transmission line. Such de-energizing is undertaken only as a last resort.
As we also describe in our published U.S. patent application Ser. No. 10/927,467, published under Publication No. 2005/0133244A1 on Jun. 23, 2005 for Live Conductor Stringing and Splicing Method and Apparatus, typically, alternating current is generated in a three-phase configuration. The three phases, B phase and C phase are all transported over separate conductors. Each such separate single phase conductor may be referred to in the industry as a phase. It is appreciated by one skilled in the art, that in some systems, more than one conductor (referred to herein as sub-conductors) carries the power load for a particular phase. This may be done in instances when a load is greater that a single conductor can accommodate. In such cases multiple (bundled) sub-conductors are often located next to each other and may hang from the same insulator as shown herein in FIG. 1. The conductors may be separated by spacers. Single insulators may be configured to carry double sub-conductors, two sub-conductors per phase, under a single yoke plate attached to the insulator.
Power lines consist of one, two or three phase systems. Each phase is electrically different from the other, that is they are at different electrical potentials. For example: in a simple house circuit of 120/240 volts, you have 3 wires (or conductors), two phase wires and a neutral or ground wire. The voltage or potential difference between the two phase wires and the neutral is 120 volts and the difference between the two phase wires is 240 volts. This is a two phase system. In a single phase system you have two wires or conductors, one at an electrical potential and the other at ground or neutral potential. In a three phase system there are three wires all at a different electrical potential from the other. Some systems may have a fourth ground or neutral wire which is electrically at the same potential difference from the phases or three wires.
Conductors are the wires or power lines in a power system. Each phase of a power line may consist of 1, 2, 3, 4 or 6 wires or conductors which are referred to as sub-conductors. Each sub-conductor is at the same electrical potential as the others regardless of the number of sub-conductors. Generally sub-conductors are used at the higher voltages (EHV) up to 765 kV and are larger and heavier.